Ultra-hard materials such as polycrystalline diamond (PCD) and PCD elements formed therefrom are well known in the art. Conventional PCD is formed by combining diamond grains with a suitable solvent catalyst material to form a mixture. The mixture is subjected to processing conditions of extremely high pressure/high temperature, where the solvent catalyst material promotes desired intercrystalline diamond-to-diamond bonding between the grains, thereby forming a PCD structure. The resulting PCD structure produces enhanced properties of wear resistance and hardness, making PCD materials extremely useful in aggressive wear and cutting applications where high levels of wear resistance and hardness are desired.
Solvent catalyst materials typically used in forming conventional PCD include metals from Group VIII of the Periodic table, with cobalt (Co) being the most common. Conventional PCD can comprise from 85 to 95% by volume diamond and a remaining amount of the solvent catalyst material. The solvent catalyst material is present in the microstructure of the PCD material within interstices that exist between the bonded together diamond grains.
A problem known to exist with such conventional PCD materials is that they are vulnerable to thermal degradation during use that is caused by differential thermal expansion characteristics between the interstitial solvent catalyst material and the intercrystalline bonded diamond. Such differential thermal expansion is known to occur at temperatures of about 400° C., which can cause ruptures to occur in the diamond-to-diamond bonding that can result in the formation of cracks and chips in the PCD structure.
Another form of thermal degradation known to exist with conventional PCD materials is also related to the presence of the solvent metal catalyst in the interstitial regions and the adherence of the solvent metal catalyst to the diamond crystals. Specifically, the solvent metal catalyst is known to cause an undesired catalyzed phase transformation in diamond (converting it to carbon monoxide, carbon dioxide, or graphite) with increasing temperature, thereby limiting practical use of the PCD material to about 750° C.
Attempts at addressing such unwanted forms of thermal degradation in conventional PCD are known in the art. Generally, these attempts have involved techniques aimed at treating the PCD body to provide an improved degree of thermal stability when compared to the conventional PCD materials discussed above. One known technique involves at least a two-stage process of first forming a conventional sintered PCD body, by combining diamond grains and a solvent catalyst material, such as cobalt, and subjecting the same to high pressure/high temperature process, and then subjecting the resulting PCD body to a suitable process for removing the solvent catalyst material therefrom.
This method produces a PCD body that is substantially free of the solvent catalyst material, hence is promoted as providing a PCD body having improved thermal stability, and is commonly referred to as thermally stable polycrystalline diamond (TSP). A problem, however, known to exist with such TSP is that it is difficult to achieve a good attachment with the substrate by brazing or the like, due largely to the lack of the solvent catalyst material within the body.
The existence of a strong attachment between the substrate and the TSP body is highly desired in a compact construction because it enables the compact to be readily adapted for use in many different wear, tooling, and/or cutting end use devices where it is simply impractical to directly attach the TSP body to the device. The difference in thermal expansion between the TSP body and the substrate, and the poor wettability of the TSP body diamond surface due to the substantial absence of solvent catalyst material, makes it very difficult to bond the TSP body to conventionally used substrates by conventional method, e.g., by brazing process. Accordingly, such TSP bodies must be attached or mounted directly to the end use wear, cutting and/or tooling device for use without the presence of an adjoining substrate.
When the TSP body is configured for use as a cutting element in a drill bit for subterranean drilling, the TSP body itself is mounted to the drill bit by mechanical or interference fit during manufacturing of the drill bit, which is labor intensive, time consuming, and which does not provide a most secure method of attachment.
It is, therefore, desired that an ultra-hard material construction be developed that includes an ultra-hard material body having improved thermal stability when compared to conventional PCD materials, and that accommodates the attachment of a substrate material to the ultra-hard material body so the resulting compact construction can be attached to an application device, such as a surface of a drill bit, by conventional method such as welding or brazing and the like.